Local officials in southern Afghanistan say an air strike has killed at least 21 civilians, including women and children. The U.S. military says it was fighting Taleban insurgents in the area, but it has not confirmed any civilian casualties. VOA correspondent Benjamin Sand reports from Islamabad that the incident is the latest fueling Afghan concerns about international military operations.

The governor of Helmand province says the civilians were killed Tuesday evening after insurgents in the isolated Sangin Valley district sought refuge inside villagers' homes during heavy combat.

NATO and U.S. special forces are targeting Taleban insurgents in the area, and fighting throughout the district has intensified in recent days.

U.S. military spokesman, Major Chris Belcher, says a number of militants were killed in the fighting, but he says there are no confirmed reports of civilian deaths.

"If we receive confirmed reports of civilian casualties, of course we will investigate it," he said. "We take all reports of civilian casualties seriously, and we do everything in our operations to prevent civilian casualties."

Major Belcher says the fighting erupted after suspected Taleban insurgents opened fire on Afghan soldiers and U.S. special forces on patrol.

The Sangin valley is considered a Taleban stronghold as well as a major center for illegal opium production.

As NATO forces struggle to regain control of the district, military officials say civilian casualties are eroding public support for the international mission in Afghanistan.

Violent anti-American protests broke out in the western province of Herat last week after local authorities there said 51 civilians were killed.

On Tuesday, a U.S. military commander issued a public apology to families of Afghan civilians killed by American Marines following a suicide bombing earlier this year.

The commander called the killing of innocent Afghans by American troops "a terrible stain" on America's honor and acknowledged civilian casualties are hurting the military's image in Afghanistan.

Afghan President Hamid Karzai has repeatedly condemned the loss of innocent lives, most recently during a nationally televised speech last week.

"We can no longer accept our civilian casualties," Karzai said. "We can no longer accept it. We are very sorry when an international coalition force NATO soldier loses his life or is wounded, but Afghans are human beings too."

Afghan politicians say they are under increasing pressure to act.

On Tuesday, the country's upper house of Parliament passed a bill demanding an end to international military operations unless they are first coordinated with the Afghan government or the international forces come under direct attack.

The bill, which still needs to be passed by the lower house before the president can sign it into law, also called for direct talks with the Taleban.